1. Technical Field
The present invention relates to a cooling unit manufacturing method, cooling unit, optical device and projector.
2. Related Art
The cooling units using cooling fluid include those having a cooling plate in a structure arranged with a metal pipe as a cooling-liquid passageway between the inner surfaces of a pair of metal plates assembled oppositely. This cooling plate is manufactured by forming a pipe receiving groove greater than the metal pipe in at least one of the one pair of metal plates and assembling the metal pipe and the one pair of metal plates integrally. During the manufacturing process, a pressurized fluid is supplied in the metal pipe after the assembling. By expanding the diameter of the pipe, the metal pipe is closely contacted with the pipe-receiving groove (see JP-A-2002-156195, for example).
In the cooling unit manufacturing method, the pipe-receiving groove is formed inverted taper with respect to the mating surface. During expanding the diameter of the metal pipe, the groove edge (undercut) is bitten in the metal pipe thereby joining the metal plate and the metal pipe together.
However, in the manufacturing method, there is a need for conducting a machining with the use of an especial cutting tool in forming the undercut, making it difficult to reduce the cost.
Meanwhile, in order to place the metal pipe in good contact with the receiving groove, the process of metal pipe diameter expansion must be divided and repeated a plurality of number of times. This however requires a long time.
Furthermore, where the metal pipe is small in diameter, the pipe is difficult to expand the diameter thereof. Moreover, uneven deformation is ready to occur on the pipe, a gap is possibly caused between the pipe and the receiving groove. As a result, the cooling capability is likely to lower in the cooling plate.